Input of the study of carbonate-rich paleosols and specific climofunctions to paleoenvironmental and paleoclimatic reconstructions : application to the oligo-miocene alluvial successions of Western Europe

Abstract : Through the study of alluvial Calcisols from the Digne-Valensole (SE France) and the Loranca (central Spain) basins, the aim of this thesis is to develop specific methods and to propose new paleoenvironmental and paleoclimatic data for Western Europe.These paleosols were investigated by pedological, sedimentological, mineralogical and geochemical methods. These highlight leaching and fersiallitisation as major processes in the formation of these profiles, and the influence of the lateral variations of parent materials on paleosols features. Moreover, the cross study of paleosols and sedimentary deposits allows their integration in a high-resolution sequence stratigraphy model, and opens a discussion about the estimation of aggradation rate from alluvial successions.New climofunctions based on major elements contents and distributions through these profiles are also proposed from the study of modern analogs from NE Spain. These functions include a ratio between the subsurface horizon and the upper part of parent material to avoid bias due to the strong heterogeneity of the altered deposits. These are complementary to previous methods developed from the morphological study of calcium carbonate accumulation horizon, which permit to estimate mean annual precipitations and their seasonality, bringing the possibility to quantify mean annual temperatures and precipitations even with truncated profiles, frequent in such successions.Their application to the studied paleosols reveals a relatively hot climate with a strong seasonal contrast in terms of precipitations, similar to the modern Mediterranean climate. These data improve our knowledge of this period that paleontological studies qualify as more humid, and raise the question about the recording of climatic signal according to the considered object. Indeed, if the preservation of fossils is usually linked to humid conditions, soils form over the emerged parts of environment and record drier conditions, which justify the need to enhance the use of paleopedological studies in such reconstructions.